Actually, I usually use stock images than textures. You can find them on weheartit (I suggest you to download them from heartsswell and _evey) and also from deviantart (carllton, evey-v, etc). Those sites provide a lot of stock packs. And for the textures, I got from evey_v, krypteriahg, carllton, and many users from deviantart.

If you want to make a sad themed poster, don’t assume that you must to use sad themed texture too. You can combine all textures as long as they are appropriate with the theme. It’s better if you also experiment with the colorings.

I hope it can help you. Just ask me if you have questions. Anyway, nice to meet you! 😉